133 research outputs found
Tunable mechanical and thermal properties of ZnS/CdS core/shell nanowires
Using all atom molecular dynamics (MD) simulations, we have studied the
mechanical properties of ZnS/CdS core/shell nanowires. Our results show that
the coating of a few atomic layer CdS shell on the ZnS nanowire leads to a
significant change in the stiffness of the core/shell nanowires compared to the
stiffness of pure ZnS nanowires. The binding energy between the core and shell
region decreases due to the lattice mismatch at the core-shell interface. This
reduction in binding energy plays an important role in determining the
stiffness of a core/shell nanowire. We have also investigated the effects of
the shell on the thermal conductivity and melting behavior of the nanowires
Glassy swirls of active dumbbells
The dynamics of a dense binary mixture of soft dumbbells, each subject to an
active propulsion force and thermal fluctuations, shows a sudden arrest, first
to a translational then to a rotational glass, as one reduces temperature
or the self-propulsion force . Is the temperature-induced glass different
from the activity-induced glass? To address this question, we monitor the
dynamics along an iso-relaxation-time contour in the plane. We find
dramatic differences both in the fragility and in the nature of dynamical
heterogeneity which characterise the onset of glass formation - the
activity-induced glass exhibits large swirls or vortices, whose scale is set by
activity, and appears to diverge as one approaches the glass transition. This
large collective swirling movement should have implications for collective cell
migration in epithelial layers.Comment: 13 pages, 11 figure
Activity controls fragility: A Random First Order Transition Theory for an active glass
How does nonequilibrium activity modify the approach to a glass? This is an
important question, since many experiments reveal the near-glassy nature of the
cell interior, remodelled by activity. However, different simulations of dense
assemblies of active particles, parametrised by a self-propulsion force, ,
and persistence time, , appear to make contradictory predictions about
the influence of activity on characteristic features of glass, such as
fragility. This calls for a broad conceptual framework to understand active
glasses; here we extend the Random First-Order Transition (RFOT) theory to a
dense assembly of self-propelled particles. We compute the active contribution
to the configurational entropy using an effective medium approach - that of a
single particle in a caging-potential. This simple active extension of RFOT
provides excellent quantitative fits to existing simulation results. We find
that whereas always inhibits glassiness, the effect of is more
subtle and depends on the microscopic details of activity. In doing so, the
theory automatically resolves the apparent contradiction between the simulation
models. The theory also makes several testable predictions, which we verify by
both existing and new simulation data, and should be viewed as a step towards a
more rigorous analytical treatment of active glass
Active fluidization in dense glassy systems
Dense soft glasses show strong collective caging behavior at sufficiently low
temperatures. Using molecular dynamics simulations of a model glass former, we
show that the incorporation of activity or self-propulsion, f0, can induce cage
breaking and fluidization, resulting in a disappearance of the glassy phase
beyond a critical f0 . The diffusion coefficient crosses over from being
strongly to weakly temperature dependent as f0 is increased. In addition, we
demonstrate that activity induces a crossover from a fragile to a strong glass
and a tendency for clustering of active particles. Our results are of direct
relevance to the collective dynamics of dense active colloidal glasses and to
recent experiments on tagged particle diffusion in living cells.Comment: 8 pages, 9 figure
Down regulation of membrane-bound Neu3 constitutes a new potential marker for childhood acute lymphoblastic leukemia and induces apoptosis suppression of of neoplastic cells
Membrane-linked sialidase Neu3 is a key enzyme for the extralysosomal catabolism of gangliosides. In this respect, it regulates pivotal cell surface events, including trans-membrane signaling, and plays an essential role in carcinogenesis. In this report, we demonstrated that acute lymphoblastic leukemia (ALL), lymphoblasts (primary cells from patients and cell lines) are characterized by a marked down-regulation of Neu3 in terms of both gene expression (-30 to 40%) and enzymatic activity toward ganglioside GD1a (-25.6 to 30.6%), when compared with cells from healthy controls. Induced overexpression of Neu3 in the ALL-cell line, MOLT-4, led to a significant increase of ceramide (+66%) and to a parallel decrease of lactosylceramide (-55%). These events strongly guided lymphoblasts to apoptosis, as we assessed by the decrease in Bcl2/Bax ratio, the accumulation of Neu3 transfected cells in the sub G0-G1 phase of the cell cycle, the enhanced annexin-V positivity, the higher cleavage of procaspase-3. Therefore, the reduced expression of Neu3 in ALL could help lymphoblasts to survive, maintaining the cellular content of ceramide below a critical level. Interestingly, we found that Neu3 activity varied in relation to disease progression, increasing in clinical remission after chemotherapy, and decreasing again in patients that relapsed. In addition, a negative correlation was observed between Neu3 expression and the percentage of the ALL marker 9-OAcGD3 positive cells. Consequently, Neu3 could represent a new potent biomarker in childhood ALL, to assess the efficacy of therapeutic protocols and to rapidly identify an eventual relapse
Is the outcrop topology of dolerite dikes of the Precambrian Singhbhum Craton fractal?
In the Precambrian Singhbhum Craton of eastern India, newer dolerite dikes occur profusely with varying outcrop lengths. We have analysed the nature of their length-size and orientation distributions in relation to the theory of fractals. Two orientational sets of dikes (NW-SE and NE-SW) are present. Both the sets show strongly non-power-law size distributions, as reflected in non-linear variations in logarithmic space. We analyzed thousands of data, revealing that polynomial functions with a degree of 3 to 4 are the best representatives of the non-linear variations. Orientation analysis shows that the degree of dispersions from the mean trend tends to decrease with increasing dike length. The length-size distributions were studied by simulating fractures in physical models. Experimental fractures also show a non-power-law distribution, which grossly conforms to those of the dolerite dikes. This type of complex size distributions results from the combined effects of nucleation, propagation and coalescence of fractures
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